Electrolytic oil purifying method

ABSTRACT

Sulfur is removed from liquid hydrocarbon oils such as crude oil by subjecting a mixture of the oil and an electrolyte to a direct current field at a relatively high current and low voltage for causing oxidation, reduction or other electrochemical reaction of the sulfur or sulfur-containing material enabling ready separation and removal of the sulfur from the oil.

' United States Patent Bell et a1.

Oct. 28, 1975 ELECTROLYTIC OIL PURIFYING METHOD FOREIGN PATENTS ORAPPLICATIONS 2,229 5/1883 United Kingdom 204/136 139,233 3/1920 UnitedKingdom 204/136 Primary E,\'aminerR. L. Andrews Attorney, Agent, orFirm-J. Wesley Haubner [57] ABSTRACT Sulfur is removed from liquidhydrocarbon oils such as crude oil by subjecting a mixture of the oiland an electrolyte to a direct current field at a relatively highcurrent and low voltage for causing oxidation, reduction or otherelectrochemical reaction of the sulfur or sulfur-containing materialenabling ready separation and removal of the sulfur from the oil.

5 Claims, N0 Drawings ELECTROLYTIC OIL PURIFYING METHOD The presentinvention relates to the removal of sulfur from hydrocarbon liquids,especially hydrocarbon oils such as crude oil.

It is an object of the present invention to reduce the sulfur content ofhydrocarbon liquids, particularly crude oil.

It is another object of the invention to provide a process for purifyingcrude oil and other hydrocarbon liquids which is readily carried out atrelatively low cost.

A particular object of the invention is to provide a process of theabove type wherein the sulfur content is reduced by electrochemicalmeans.

Other objects and advantages will become apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention in one of itsaspects relates to the method of electrochemically removing sulfur fromhydrocarbon liquids including sulfur-containing materials whichcomprises mixing the hydrocarbon liquid with an ion-producing compoundselected from the group consisting of inorganic electrolytes andionizing organic solvents, and subjecting the thus obtained mixture toan electrical DC field having a voltage in the range of about 2 to 120volts and a current of at least about 0.001 amperes per squarecentimeter, and recovering the hydrocarbon liquid in which thesulfur-containing materials have been substantially reduced.

In general, it has been found in accordance with the invention that theuse of relatively high current at low voltages in the electrolyte-oilmixture promotes the oxidation (or reduction, as the case may be) ofsulfur contaminants in the oil, resulting in precipitation orvolatilization of sulfur compounds which are thereby removed from theoil mixture.

As will be understood, the sulfur components in crude oil may be ofvarious types. It is known that the sulfur content of petroleum may varyfrom less than 0.1% to by weight depending upon the source. This sulfurmay be present as free sulfur. hydrogen sulfide, mercaptans, disulfides,cyclic sulfides or thiophenes. The present refinery methods for removalof sulfur, such as hydro-desulfurization, require the use of relativelycumbersome apparatus and expensive processes. The electrochemicalprocess of this invention, on the other hand, is a relatively simpleinexpensive desulfurization method. 5

In the electrolysis of any particular oil-electrolyte mixture to producean electrochemical reaction in accordance with the invention, under thesame conditions certain sulfur compounds may be oxidized, others may bereduced, some may be precipitated, some may be volatilized and othersmay be deposited on the electrode surfaces. From experiments carried outin the course of practicing the invention, it appears that oxidation isthe predominant reaction. and oxidation products such as sulfonic acidsand sulfur oxides have been identified. The reduction of sulfurcompounds has been indicated by the production of H 5 volatilized duringthe process.

The removal or reduction of sulfur in accordance with the principles ofthe invention may be carried out using various sulfur-containinghydrocarbon liquids or oils mixed with various ion-producing compounds.For example. hydrocarbons such as mineral oil and crude 2 oil fromvarious geographical sources have been satisfactorily treated by theelectrochemical process of the invention.

The inorganic electrolyte with which the hydrocarbon liquid maybe mixedmay be in the form of an aqueous solution of a salt or alkali base inconcentrations high enough to obtain an electrically conducting system.Such solutions may contain. for example, a salt or base such as sodiumchloride, lithium chloride, potassium chloride, strontium chloride,sodium nitrate, lithium nitrate, potassium nitrate, sodium carbonate,potassium carbonate, calcium carbonate, barium carbonate, sodiumhydroxide, potassium hydroxide. calcium hydroxide. and barium hydroxide.

Ionizing organic solvents which may be used in combination with thehydrocarbon liquid include methanol, benzene, nitrobenzene, toluene,xylene, and glacial acetic acid. Many other inorganic and organiccompounds will also be found suitable for use in practicing the presentinvention.

In general, the electrolysis of the oil-electrolyte mixture is carriedout in a DC electrical field having a voltage in the range of about 2 to120 volts and a current of between .001 to 25 amperes per squarecentimeter, with a preferred voltage range of about 2 to 10 volts beingused in most cases. The concentration of the ionizing compound employedin the mixture will depend mainly on the spacing, surface area andconfiguration of the electrodes. For any particular conditions, theamount of the ionizing material used should be such to provide aconductivity which results in a voltage of the system in the range setforth above.

The process of the present invention will be illustrated by thefollowing examples, it being understood that the invention is notintended to be limited thereby. In the experiments described below, theelectrolysis was carried out in a ml flask equipped with two standardplatinum electrodes. The anode was a cylinder of platinum mesh /2" indiameter and 2" long. The cathode was a mesh cylinder 1%" in diameterand 2" long.

EXAMPLE I A 43.88 gram sample of crude oil designated Fleisher Lease oilcontaining 6.13% by weight of sulfur was mixed with 54.06 grams ofdistilled water containing 1.08 grams of reagent grade NaOH. Themixture, which had a pH of 10, was subjected to electrolysis carried outin the above described reaction vessel. The mixture was subjected to aDC electrical field of 0.l000.l75 amperes, for a total of 64 hours.While holding the current to a maximum of 0.175 amperes during the run,the voltage varied between 25 and 200 volts. At the termination of thisexperiment. it was found that the sulfur content in the oil had beenreduced to 4.57%.

EXAMPLE II A mixture of 7. 14 grams of crushed limestone. 49.73 gramsdistilled water, 43.03 grams of No. 6 fuel oil, and 048 gram Ca(OH). and38.78 grams distilled water was placed in the reaction vessel. Themixture separated into an oil layer and water layer. A DC current of lampere was passed through the system at 15 volts for nearly 12 hours. atwhich time the current had dropped to 0 and the voltage rose to 45volts. The sulfur content in the oil layer before the electrolysis beganwas found to be 086%. whereas at the end of the experiment the sulfurcontent was 0.60%.

EXAMPLE 111 In this experiment, 46.7 grams of No. 6 fuel oil and 4.55grams calcium hydroxide were added to 76.58 grams distilled water. andthe mixture was heated to reflux without stirring. A direct current of 1ampere at 9 volts was passed through the solution. The current droppedto within 50 minutes. At this time a surfactant, available commerciallyunder the name Triton X- 100, was added to the mixture, and electrolysiswas again initiated at 1 ampere and 20 volts. After 4 hours and 20minutes the voltage had increased to 50 volts at l ampere. The systemwas allowed to run overnight, during which time the current dropped to0.4 ampere and the voltage increased to 120 volts. The sulfur content ofthe oil layer before the experiment was 0.86%. and after the experimentwas found to be 0.51%.

EXAMPLE IV To a solution consisting of 92.55 grams distilled water, 0.39gram Ca(OH and 5.7 grams limestone. there was added 38.75 grams No. 6fuel oil cut with 10% by weight of pentane to reduce viscosity. Thesystem was subjected to electrolysis at an initial current of 1 ampereand 7 volts. During a period of 6 hours. the cur rent fell to 0 and thevoltage increased to 75 volts. The sulfur content of the oil layer was086% before the experiment and was found to be 0.49% after theexperiment.

EXAMPLE V A solution of 1.13 grams Triton X-100, 126.83 grams water and10.39 grams calcium hydroxide was mixed with 73.95 grams No. 6 fuel oil.The reaction mixture was heated to reflux and electrolysis was startedat l ampere and volts. Within 2 minutes the voltage had increased to 120volts and the current dropped to 0.4 ampere. An additional amount of2.14 grams Triton X-100 was added and electrolysis continued at 1 ampereand 20 volts. After 3 hours the current had dropped to 0.4 ampere andthe voltage increased to 120 volts. Again, 2.15 grams Triton X-l00 wasadded and the electrolysis continued at 0.5 ampere and 120 volts. Within3 hours, the current dropped to 0.2 ampere and the voltage remained at120 volts. Before the experiment the sulfur content of the oil layer was0.86% and after the experiment it was 0.54%.

EXAMPLE Vl This was a control experiment which was carried out todetermine whether a reduction in sulfur content in the oil can beachieved with a similar mixture is subjected to electrolysis at muchhigher voltages.

A mixture of 122.12 grams distilled water, 10.14 grams calciumhydroxide. 4.05 grams Triton X- 100 and 73.31 grams No. 6 fuel oil wasprepared and mechanieally agitated for several days. At the end of thisperiod, the oil layer was placed in the previously described reactionvessel and subjected to a 2000 volt per centimeter DC potential forseveral hours. At the end of this period the oil was analyzed and foundto contain the same sulfur content as the original oil content of 0.86%sulfur.

EXAMPLE V11 To a mixture of 15 ml methanol and 51.13 grams mineral oilthere was added 8ce of thiophene. This mixture was subjected toelectrolysis at 0.1 ampere and 50 volts. The resistance rapidlyincreased to 30 ohms within 56 minutes and the mixture changed from aninitial colorless condition to a yellow color. Gas collected over thereaction mixture indicated SO: and mercaptans were present. Theelectrolysis was run intermittently for 4 days. During this time mlmethanol was added to maintain liquid level. A total of 8.7 ampere hoursof electricity were used. During the last two days of operation, the gasevolved from the reaction was found to contain formaldehyde.

The inside of the reaction vessel and the stirring bar and cathode werecovered with a black deposit insoluble in carbon disulfide, the totalweight of the deposit being 0.30 gram. No deposit was detected on theanode.

Analysis of the oil layer showed that initially, prior to electrolysis,the sulfur content was 2.30% while the final oil layer had a sulfurcontent of 0.625%.

EXAMPLE V111 A sample consisting of Sec thiophene. 46.12 grams mineraloil and 46.21 grams distilled water containing 1.17 grams sodiumhydroxide was mixed and electrolyzed at 0.175 ampere and 4 volts for15.4 ampere hours. The aqueous layer turned yellow and a gray depositformed on the anode, while a black deposit formed on the cathode. Abrown deposit formed and floated on top of the liquid phases. At the endof the experiment. 42.83 grams of mineral oil, 40.00 grams aqueousphase. 0.54 gram deposit on the anode, 1.23 gram deposit on the cathodeand 0.22 gram brown residue were found. Upon standing several days, theoil layer turned sky blue in color. At the start of the experiment, theoil layer had 1 24% sulfur content, and at the end it had 0.20% sulfur.During the experiment. the sulfur content of the aqueous layer hadincreased from 0 to 2.96%.

EXAMPLE 1X Into the previously described reaction vessel there wasintroduced 46.14 grams mineral oil, 47.39 grams distilled watercontaining 1.13 gram calcium hydroxide and 8cc thiophene. A total of12.86 ampere hours of DC current was passed through the system at 0.2ampere and 7 volts. A brown solid phase began to separate from themixture as electrolysis proceeded. The pH of the system was adjusted bythe addition of 1.66 grams Ca(OH) after 8.56 ampere hours of operation.Just prior to this addition, the generation of gas was noted. At thestart of the experiment, the oil layer had 2.71% sulfur and a pH of 12.At the end of the experiment. the oil layer had 0.252% sulfur and the pHwas 5.

EXAMPLE X To a 50.37 gram sample of mineral oil was added 7.75 ccdibutyl disulfide and 43.5 grams methanol. The mixture was electrolyzedat 0100-0. amperes and 50 volts for 64.5 hours or 9.97 ampere hours.During the run no deposits formed on the electrodes and no color changeswere noted in the mixture. At the start, the oil layer contained 3.75%sulfur, and at the end of the experiment it contained 2.57% sulfur.

In all of the above experiments the current density of the system wasabout 0.008 amperes/em As previously indicated. it is preferable inaccordance with the invention to employ a current density of at least0.001 amperes/cm" because it is economically impractical to operate atlower current densities, while a current density of more than amperes/cmis not feasible due to erosion of the anode surface and cavitation onthe electrode surface.

The Triton surfactant material mentioned in the Examples was used toemulsify the oil so as to reduce fouling of the electrodes, while at thesame reducing the viscosity of the mixture to enhance theelectrochemical reaction.

As a result of our experiments, it appeared to be preferable to maintainthe pH of the mixture at a relatively high level, i.e., 8-12, since itappeared that the electrochemical reaction proceeded at a more rapidrate at such a pH level. However, it is not intended to limit theprocess of the invention to mixtures of such pH levels, sincesatisfactory results are obtainable at lower pH values. In adjusting thepH by the addition of a base. it is desirable to use compounds such asCa(OH to form insoluble sulfur-containing compounds to facilitate theseparation and removal of these compounds from the mixture.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore. the appendedclaims are intended to cover all such equivalent 6 variations as comewithin the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. The method of electrochemically removing sulfur from hydrocarbonliquids including sulfur containing materials which comprises mixing thehydrocarbon liquid with an ionizing organic solvent, and subjecting thethus obtained mixture to an electrical D.C. field having a voltage ofabout 2 to volts and a current of at least about 0.00l amperes persquare centimeter. and recovering said hydrocarbon liquid in which saidsulfur containing materials have been substantially reduced.

2. The method as defined in claim 1, wherein said current is not morethan about 25 amperes per square centimeter.

3. The method as defined in claim 2, wherein said hydrocarbon liquid iscrude oil.

4. The method as defined in claim 3, wherein said ionizing organicsolvent is selected from the group consisting of methanol, benzene,toluene. Xylene and glacial acetic acid.

5. The method as defined in claim 1, wherein said hydrocarbon liquid isselected from the group consisting of crude oil, mineral oil andpetroleum and said voltage is in the range of about 2 to 10 volts.

1. THE METHOD OF ELECTROCHEMICALLY REMOVING SULFUR FROM HYDROCARBONLIQUIDS INCLUDING SULFUR CONTAINING MATERIALS WHICH COMPRISES MIXING THEHYDROCARBON LIQUID WITH AN IONIZING ORGANIC SOLVENT, AND SUBJECTING THETHUS OBTAINED MIXTURE TO AN ELECTRICAL D.C. FIELD HAVING A VOLTAGE OFABOUT 2 TO 120 VOLTS AND A CURRENT OF AT LEAST ABOUT 0.0001 AMPERES PERSQUARE CENTIMETER, AND RECOVERING SAID HYDROCARBON LIQUID IN WHICH SAIDSULFUR CONTAINING MATERIALS HAVE BEEN SUBSTANTIALLY REDUCED.
 2. Themethod as defined in claim 1, wherein said current is not more thanabout 25 amperes per square centimeter.
 3. The method as defined inclaim 2, wherein said hydrocarbon liquid is crude oil.
 4. The method asdefined in claim 3, wherein said ionizing organic solvent is selectedfrom the group consisting of methanol, benzene, toluene, xylene andglacial acetic acid.
 5. The method as defined in claim 1, wherein saidhydrocarbon liquid is selected from the group consisting of crude oil,mineral oil and petroleum and said voltage is in the range of about 2 to10 volts.